1. Technical Field of the Invention
The present invention relates generally to wireless local area networks (WLANs). More particularly, the present invention relates to a method and system for providing priority access to a WLAN to perform fast channel switching.
2. Discussion of the Related Art
In a typical 802.11 based wireless local area network (WLAN), access to the wireless medium is controlled at the MAC layer by coordination functions. The 802.11 standard provides for two coordination functions, the distributed coordination function (DCF), and the point coordination function (PCF). If contention-free service is required, it can be provided by the point coordination function (PCF), which is built on top of the DCF. The PCF is an optional part of the 802.11 specification and has not been widely implemented to date. Frame exchanges between network stations STAs under the DCF dominate currently deployed WLANs. The DCF is based on a listen-before-talk scheme referred to as CSMA/CA (carrier sense multiple access with collision avoidance) as described by the IEEE 802.11 standard, incorporated herein by reference in its entirety.
In accordance with the DCF scheme, before attempting to transmit a frame, each station checks whether the medium is idle. If the medium is not idle, the stations defer to each other and employ an exponential back-off algorithm to avoid transmission collisions.
One drawback with the DCF scheme is that network stations may incur relatively long delays in attempting to exchange frames over the wireless medium in the case of high traffic load in the network.
A consequence of these potential transmission delays is that compliance with the dynamic frequency selection (DFS) regulatory requirement for operation in the 5 GHz band in Europe may not be met. The DFS regulatory requirement stipulates, inter alia, that a wireless STA must (1) quickly halt transmissions in a current channel within a prescribed time and (2) switch channels within a prescribed time when a primary user is detected. A primary user may be, for example, a radar tracking system or a satellite system.
Thus, there is a need for an improved medium access scheme, performed at the MAC layer, to provide fast channel access to a wireless medium to quickly perform a channel switch and/or quickly stop transmissions in the current channel to prevent potential interference with mission critical functions being performed by primary users in the co-located systems.